1. Field of the Invention
The present invention relates to a speed change control apparatus of an automatic transmission capable of selecting between an auto-mode performing a speed change on the basis of a running condition and a manual mode performing a speed change on the basis of a manual manipulation.
2. Description of Related Art
As conventional speed change control apparatuses of an automatic transmission, there is one, for example, disclosed in Japanese Patent Laid Open Publication Hei No. 2-8545.
This conventional apparatus is constructed, on the basis of a shift apparatus provided in a normal automatic transmission, a manual shift function including a plus sensor outputting an up-shift signal and a minus sensor outputting a down-shift signal is added to operate such that a shift lever is moved from a "D" range position which selects a normal running to a manual shift position, and here, a speed change stage of the transmission is shifted up by one speed to a higher speed side by operating the plus sensor, conversely, the speed change stage is shifted down by one speed by operating the minus sensor.
In the conventional speed change control apparatus of an automatic transmission mentioned above, it is advantageous in that under a running condition in the auto-mode by selecting the "D" range, it is possible to perform the up-shift and the down-shift by switching to the manual mode so that the speed change stage can be selected in accordance with a preference of a driver. However, an unsolved problem is involved in that there is a fear of causing an overspeed condition of the engine due to the down-shift by the manual manipulation.
In order to solve this unsolved problem, it is considered as disclosed, for example, in Japanese Utility Model Laid Open Publication No. 61-169629, to suppress the overspeed of the engine by automatically up-shifting the automatic transmission having priority over a normal speed change judgement when it is detected or predicted that the engine will be in the overspeed condition.
However, in this case, since the up-shift to suppress the overspeed of the engine is automatically performed independent of the driver's manipulation, when the up-shift to suppress the overspeed of the engine and the up-shift in the manual mode performed by the driver's intention are duplicated or repeated within a short time period, it will result in the up-shift of two speeds, and thus, the acceleration intended by the driver is not obtained and the driver will feel discrepancy or dissatisfaction. Conversely, when the down-shift in the manual mode is performed by the driver's intention just after the up-shift to suppress the overspeed of the engine is performed, it will become impossible to suppress the overspeed of the engine, and thus posing a new problem.